Directional optimisation of a quadratic Lyapunov function

An effective way of constructing optimum Lyapunov functions is presented. This is achieved by seeking an optimum Lyapunov function for each direction in the phase space. The composite of these optimum Lyapunov functions defines the optimum region of stability.     

Enhanced ab initio protein folding simulations in Poisson-Boltzmann molecular dynamics with self-guiding forces

We have investigated the sampling efficiency in molecular dynamics with the PB implicit solvent when self-guiding forces are added. Compared with a high-temperature dynamics simulation, the use of self-guiding forces in room-temperature dynamics is found to be rather efficient as measured by potential energy fluctuation, gyration radius fluctuation, backbone RMSD fluctuation, number of unique clusters, and distribution of low RMSD structures over simulation time. Based on the enhanced sampling method, we have performed ab initio folding simulations of two small proteins, betabetaalpha1 and villin headpiece. The preliminary data for the folding simulations is presented. It is found that betabetaalpha1 folding proceeds by initiation of the turn and the helix. The hydrophobic collapse seems to be lagging behind or at most concurrent with the formation of the helix. The hairpin stability is weaker than the helix in our simulations. Its role in the early folding events seems to be less important than the more stable helix. In contrast, villin headpiece folding proceeds first by hydrophobic collapse. The formation of helices is later than the collapse phase, different from the betabetaalpha1 folding.     

Measurement and simulation of light distribution in biological tissues

Lateral light-distribution images of biologic tissues were used to study the tissues' optical characteristics. Monte Carlo simulation with the same conditions was performed to simulate the light distribution for comparison. Simulation results showed that the lateral light distribution was similar to the internal light distribution in biologic tissue. The direction of muscle fibers and the temperature both affect the near-field light distribution in tissue. The lateral view distribution can be both measured and simulated to study photon migration in tissue. It can also be used to estimate or verify the optical coefficients of tissue.     

Kuosheng BWR/6 stability analysis with LAPUR5 code

Unstable power/flow oscillation of a nuclear power reactor core is one of the main reasons that cause minor core damage. Stability analysis to determine system’s decay ratio needs to be performed at each core reload design to prevent core instability events from happening. Making use of LAPUR5 and SIMULATE-3 codes, we have established a methodology to conduct such analysis. Comparisons made with vendor’s STAIF results indicated close agreements, within acceptable ±0.2 in decay ratios, for Kuosheng NPP Unit2 Cycle 17 reloads design. Sensitivity studies have shown that density reactivity coefficient, delayed-neutron fractions (β) and decay constants (λ), total core flow, and core power axial shape are the most important parameters that might affect the accuracy of decay ratios. We have also found that core conditions at EOC result in larger decay ratios than those at BOC.     

Phase averaging and interpolation using resistor strings or resistor rings for multi-phase clock generation

Circuit techniques using resistor strings (R-strings) and resistor rings (R-rings) for phase averaging and interpolation are described. Phase averaging can reduce phase errors, and phase interpolation can increase the number of available phases. In addition to the waveform shape, the averaging and the interpolation performances of the R-strings and R-rings are determined by the clock frequency normalized by a RC time constant of the circuits. To attain better phase accuracy, a smaller RC time constant is required, but at the expense of larger power dissipation. To demonstrate the resistor ring's capability of phase averaging and interpolation, a 125-MHz 8-bit digital-to-phase converter (DPC) was designed and fabricated using a standard 0.35-/spl mu/m SPQM CMOS technology. Measurement results show that the DPC attains 8-bit resolution using the proposed phase averaging and interpolation technique.     

Stability of the warpage in a PBGA package subjected to hygro-thermal loading

The CTE and CHE mismatch between materials in a thin PBGA package is primarily attributed to the warpage which occurs when the package is being mounted on to a PCB, especially when the moisture content reaches a specified value. In this paper, the stability equations for the warpage in a PBGA package without the solder balls being subjected to hygro-thermal loading, by modeling it as an initially perfect/imperfect composite plate, have been developed. The analytical closed-form solutions are found and used to compute not only the critical moisture content but also the warpage occurring before the critical loads are reached. The buckling of the PBGA package, at the solder reflow peak temperature, occurs when the theoretical moisture content reaches 0.259–0.283 wt.%. This theoretical critical moisture content accurately predicts the experimental critical moisture content (0.25–0.30 wt.%) derived from our previous work. The results, from comparison between theoretical and experimental critical moisture content, indirectly indicate that the PBGA package has little imperfection. However, the large initial imperfect structure of the package does not easily reach the buckling stage because of moisture absorption. In addition to this, the structure of the PBGA package before buckling become stress-free at the moisture level of 0.077 wt.% and at room temperature during moisture conditioning.     

签密方案在分布式协议中的应用

该文基于可验证秘密共享思想和对Zheng的签密方案的必要修改,首次构造了一种不需要可信中心的门限签密方案．它能同时达到门限签名和加密的双重目的,实现代价仅和门限签名相当,并具有非否认性质．该文对当前一些分布式密钥分配协议做了分析,并基于Naor的基本思想,重点利用签密方案设计了协议SC—DKDS．与其它协议相比,该协议在减低实现成本等方面更为有效,因为它不需要认证信道、秘密信道及复杂的零知识证明等．该文还在RO（Random Oracle,随机预言）模型中给出了以上协议的安全性证明．     

红薯梗中清除自由基活性成分的研究

本实验将红薯梗以甲醇粗提后,再用有机溶剂梯度萃取,并测定了各组分清除DPPH•以及O2-•自由基的活性。实验结果表明,红薯梗各提取物对1,1-二苯基-2-苦肼基(DPPH•)和O2-•自由基有程度不同的清除作用。对两种自由基的清除均以乙醚组分效果最好,其中清除DPPH•的活性为同浓度茶多酚的1.6倍。提纯后的乙酸乙酯的主要组分,经紫外、可见分光光度计法的测定推测,其结构类型应为二氢黄酮类。